The chickens were already getting sick when Yoshihiro Kawaoka arrived in the U.S. in August 1983. A few months before, in April, a bird flu virus had arisen in the poultry farms of eastern Pennsylvania, but veterinarians had deemed it to be “low pathogenic”—meaning it made chickens sick but did not kill many of them. As the virus swept through the poultry farms, however, a new strain developed. Chickens began to die in large numbers, and farmers started to fear for their livelihoods. The state called in the U.S. Department of Agriculture, which set up a temporary command and control center in a strip mall outside of Lancaster. To contain the epidemic, it culled 17 million birds from Pennsylvania down through Virginia.

Kawaoka was a young researcher from Japan who was starting work at St. Jude Children’s Research Hospital in Memphis. His boss, virologist Robert Webster, had a theory that human influenza viruses originate in bird populations—that they circulate harmlessly among ducks and geese and that, every once in a while, a strain will evolve the ability to live in the human upper respiratory tract. To combat human influenza, Webster asserted, you first had to understand bird flu. In November, when Webster heard that the outbreak had become serious, he dropped everything and headed to its epicenter.